2004 CSSA Trials Q18 (1 Viewer)

[Cobra]

Hey fellaz, im going to need help with this question.....

Observer A sits in the middle of a train traveling at high speed past a railway station as shown in the picture below (sorry, no picture available). Observer B stands on the station platform. Lightning strikes the front and back of the train at the moment observer A passes observer B. Analyse the statements of both observers regarding the order of the lightning strikes.

Like, i understand the situation where you have operator switching the light on which trigger two light sensitive doors, compared with the observer, but with this situation, does observer B see the lightning at the back of the train strike first because its accelerating towards him and the lightning at the other end which is accelerating away, takes longer for it to get to him, thus striking later?

Helllllpppppp....

 

[Cobra]

someone must be able to help me with this.....

 

[zeek]

Observer A sees the lightning strike the train simultaneously because he is in the inertial frame of reference. Observer B sees the lightning occur simultaneously, but i think he sees only the front being struck by lightning as length contraction predicts that the train carriage will shorten, and the lightning at the back should miss the carriage... but then that probably doesn't make sense
Im pretty sure you can safely rule out that the lightning occurs at the same time, so you won't see one lightning hit first before the other as both observers are in the inertial frame of reference where the lightning occurs (the train station).
I hope that helps

 

[gamecw]

the lightning at the back should miss the carriage... but then that probably doesn't make sense

but the question says:
Lightning strikes the front and back of the train at the moment observer A passes observer B.

so i dont think it missed back carriage since it says it did hit...

mm im not sure if im right but heres what i think wud happen:

Observer B sees lightin strikes the front and back simtaneiously whereas Observer A sees lightin strikes front 1st, then take sum time to see the lightin strikes the back... This is because lightin strikes the train occurs in Observer B's inertial frame of reference (outside of train). Observer A is moving relative to the lighting. So right afta the lightin strikes the train, observer A moves towards the front light source, hence sees it 1st, then take sometime to see the lighting hit the back door..
this is simliar to Einstein's thought experiment with the light in the the mid of trian.. the only difference is, this time light strikes from outside of the train.

 

[gamecw]

sumone has the solution? i wana kno the answer.

 

[zeek]

So right afta the lightin strikes the train, observer A moves towards the front light source, hence sees it 1st, then take sometime to see the lighting hit the back door..

How can he see one lightning hit first while the other one is delayed if they both travel at the same speed of light Even if that were to happen aren't you assuming that the train is stationary? Because, otherwise, the train would have moved infront of the lightning strike behind it before it could hit it

 

[zeek]

Well im going to have to say that they both see the lightning strikes the carriage at the same time. Reason being is that the lightning occurs in an inertial frame of reference where both observers are and because the question says that lightning strikes the back and front.

 

[gamecw]

Well im going to have to say that they both see the lightning strikes the carriage at the same time. Reason being is that the lightning occurs in an inertial frame of reference where both observers are and because the question says that lightning strikes the back and front.

light doesnt occur in an inertial frame of reference for Observer A right? since he's moving relative to the station platform, and the lightin strikes the train from 'outside' - hence from a different frame of reference?

 

[zeek]

Well you can define Observer A a new intertial frame of reference that suits both A and B. A is in relative motion to the lightning strike and so is B, therefore, they are in the same inertial frame of reference.

If the question says that both strikes hit the train at both ends then i think we can safely assume that the train is not travelling at light speed because otherwise, length contraction would have been observed and observer B should have seen the lightning strike from behind miss, but obviously this doesn't happen.

 

[gamecw]

Well you can define Observer A a new intertial frame of reference that suits both A and B. A is in relative motion to the lightning strike and so is B, therefore, they are in the same inertial frame of reference.

this confuses me lol

 

[gamecw]

How can he see one lightning hit first while the other one is delayed if they both travel at the same speed of light Even if that were to happen aren't you assuming that the train is stationary? Because, otherwise, the train would have moved infront of the lightning strike behind it before it could hit it

Q says
Lightning strikes the front and back of the train at the moment observer A passes observer B

the train is still moving, just it happens that the lightin hits the train Right when it goes pass observer B right? so i dont think u shall assmue that the train is stationary...

 

[zeek]

i meant to say that "I think yop're assuming that the train is stationary" but obviously you aren't Still though, i think that they would have to either strike at the same time because it doesn't look like the train is travelling at relativistic speeds.

About the new reference frame....

Both observer A and B are ultimately in the station, but it just so happens that observer A is experiencing motion of some sort while B isn't. So we can say that relative to the lightning bolt, A is in motion while B isn't. Thus, this is a new frame of reference.
We know that if two or more observers are in the same frame of reference, then they observe the same thing. Hence, when the lightning "strikes" observer A, the front and behind of the carriage will be struck at the same time, and observer B will see this occuring at the same time as well.

 

[gamecw]

Both observer A and B are ultimately in the station, but it just so happens that observer A is experiencing motion of some sort while B isn't. So we can say that relative to the lightning bolt, A is in motion while B isn't. Thus, this is a new frame of reference.
We know that if two or more observers are in the same frame of reference, then they observe the same thing. Hence, when the lightning "strikes" observer A, the front and behind of the carriage will be struck at the same time, and observer B will see this occuring at the same time as well.

yea ur right.. i finally figured that out when i was in shower lol.. jus came online to say that i think ur right...

 

[Cobra]

So what you're saying is, that both observers see the lightning strike at the same time?

 

[zeek]

yea thats what im gna have to say

 

[Jase]

First assume that the 'source of light' isn't from the lightning actually hitting the train and causing new radiation. The flash is from the lightning itself. In this case, assuming that A and B are at the same distances away from both bolts:

Observer A sees the the front of the train get struck first since observer A is moving during the time light from the lightning bolt is travelling to him.

Observer B sees both strikes at the same time since the lightning bolts technically travel the same distance to him.

Relativity of Simultaneity questions never really change much.

 

[Shady01]

I agree with Jase, Obersver B watching from the outside is not affected by any of the shit that affects observer A, he therefore sees it happen at same time. And oberserver A is pretty straight forward he is affected by all the effects of being in a train that is going incredably fast.

 

[jeremyandrews]

Cobra mate,
oberver B will see the lightning at the back off the train first because the train( Observer A) is moving with relative velocity to his position. Becuase of this relative velocity the distance the light from the back of the train travels to reach him is LESS than the distance the lightning at the front must travel to reach him.Thus observer A sees the event occur simultaneously due to the lightning strikes both travelling an equal distance to reach him, but B sees the one at the back first because it travels a shorter distance than A.

 

[Shady01]

Jeremy you forgot though its at the time Observer A passes Obersver B therefore their distances are equal from the lightning. And I'm not sure but doesn't einstein do a thought experiment with a guy in a train seeing light hit his train outside? I don't think Observer A ever sees anyhting simultaneously? becuase of his speed

 

[Cobra]

Cobra mate,
oberver B will see the lightning at the back off the train first because the train( Observer A) is moving with relative velocity to his position. Becuase of this relative velocity the distance the light from the back of the train travels to reach him is LESS than the distance the lightning at the front must travel to reach him.Thus observer A sees the event occur simultaneously due to the lightning strikes both travelling an equal distance to reach him, but B sees the one at the back first because it travels a shorter distance than A.

yeh, thats what i thought, because in HSC questions, i wouldn't ever expect them to ask a question where both observer a and b would see it at the same time..